The invention concerns a method for controlling the transfer of a product stack in a packaging machine, wherein the product stack is built up from n products during one work cycle TA, and is subsequently transferred by means of a transfer device into a cell of a continuously moved conveyor during a transfer cycle TT, wherein the product stack that is located in the transfer device and the cell of the conveyor assume a predetermined relative position at least at the end of the transfer cycle TT.
A packaging machine has a plurality of work stations or components that are moved relative to each other in a predetermined relationship with respect to time and space. Some components are thereby moved in cycles, i.e. after a transport movement by a predetermined length, the conveyor belts or chains remain still for a predetermined time period. The clocked movement therefore comprises alternating movement or transport phases and standstill phases.
A packaging machine also has several components or work stations that are driven in a continuous fashion, i.e. have no standstill phases, and are usually moved at a constant speed during normal interference-free operation of the packaging machine.
A packaging machine is described below by way of example, wherein a product to be packed is transported on a supply belt that is driven in a cyclic fashion to a stacking station, in which a product stack of n individual products is built up from successively arriving individual products, e.g. blister strips. As soon as the product stack has reached the predetermined desired number of individual products, it is inserted by a transfer device into a cell of a continuously driven product conveyor of a cartoning machine during a transfer cycle TT. Continuously operating cartoning machines are advantageous compared to intermittently operating cartoning machines, in that they can be operated with higher efficiency and the product stack can be inserted into a folding box in a soft, smooth and thereby interference-free fashion. Moreover, a continuously operating cartoning machine eliminates strong decelerating and accelerating motions, which reduces the risk that the product stack falls over.
The product conveyor of the cartoning machine consists of an endless circumferential conveyor belt or a corresponding conveyor chain, the outer side of which has a plurality of chamber-like cells into each of which one product stack can be inserted. Successive cells have the same separation from each other and are defined by cell walls or boundaries that project past the outer side of the conveyor. During passage of a deflecting roller, the cells open to such an extent that the product stack can be laterally inserted into the opened cell in the running direction of the conveyor at the height of the transport plane. When the deflecting roller has been passed, the cells that have received a product stack close to such an extent that the product stack is reliably grasped by the cell walls and further transported with the conveyor.
During normal operation of the packaging machine, the individual products are continuously supplied in a cyclic fashion to the stacking station, in which a product stack is formed within one work cycle TA. At the end of each work cycle TA, a new product stack is provided, which is transferred by the transfer device to the respectively associated cell of the continuously operating conveyor within one transfer cycle TT. In this fashion, the conveyor can be driven at a constant speed of motion.
During production of the individual products, it may happen that individual products are detected as being faulty and are therefore discarded. This may happen e.g. when a blister strip is not or is not completely filled or has turned out to be improperly sealed or have other faults. When a faulty product is detected, it is removed from the packaging process and upstream of the stacking station, thereby generating a hole in the line of successive products. As a result thereof, it takes four instead of three partial cycles, i.e. one partial cycle more, to build up a product stack that consists of e.g. three products in the stacking station, since one blister strip is missing at one position of the supply belt. In conventional packaging machines, an empty space in the product line that is generated by removing a detected faulty product, is filled with replacement products that are maintained in a storage device in order to prevent such irregularities. This method ensures that a continuous line of individual products arrives at the stacking station, and that the product stack can therefore always be built up within the predetermined work cycle TA.
The intermediate storage of replacement products is, however, very complex in terms of process engineering, and automatic refilling of the product line with replacement products also requires great apparative expense and therefore high costs.
It is the underlying purpose of the invention to provide a method for controlling the transfer of a product stack in a packaging machine that facilitates formation of a product stack and its transfer to a continuously operating conveyor.